Fractionation of oils by selective extraction



July 16, 1963 H. P. A. GROLL 3,

FRACTIONATION OF OILS BY SELECTIVE EXTRACTION Filed Aug. 23, 1954 5 Sheets-Sheet 1 STRIPPER.

STRIPPCR TANK TANK.

MIXER V V a, M

1: V TANK 4 DISTILLATION COLUMN INVENTOR a:

HERBERT PA. GRoLL BY W r ATTORNEYS July 16, 1963 H. P. A. GROLL 3,098,034

FRACTIONATION OF OILS BY SELECTIVE EXTRACTION Filed Aug. 23, 1954 s Sheets-Sheet 2 IDISTILLATION 1 An ,DISTILLATION COLUMN 5135: co LUM N 1N VENTOR HERBERT PA; GRoLL BY W /9% ATTORNEYS July 16, 1963 H. P. A. GROLL 3,093,034

FRACTIONATION OF OILS BY SELECTIVE EXTRACTION Filed Aug. 25, 1954 5 Sheets-Sheet 5 ols'rlLLA'rlor -DIVSTILLATION COLUMN COLUMN Q9 133 L2 0 "733a.

" M v A /-34 //.9 /34a 85 w o IN VENTOR HERBERT PA. GRoLL BY w ATTORNEYS July 16, 1963 H. P. A. GROLL 3,098,034

FRACTIONATION OF OILS BY SELECTIVE EXTRACTION Filed Aug. 23, 1954 5 Sheets-Sheet 4 DISTILLATION 86 r-uacov ERY TANK MIXER FILTER TANK 0 60a. 80b a0;

INVENTOR HERBERT PA. GRoLL ATTORNEYS July 16, 1963 H. P. A. GROLL 3,098,034

FRACTIONATION 0F OILS BY SELECTIVE EXTRACTION Filed Aug. 23, 1954 5 Sheets-Sheet 5 SOLVENT FOR. COOLER- RECIRCULATION COOLE 0 STRIPPER Q PARATOR SE PARATO STRIPPER Q COOLER OOLER COOLER SEPARATOR 2B MIXER.

HEATER EATER "EATER o e m o I o 0 A 0 m d m A 8) 0 A A 0 0 m 0 O'L SOLVENT SOLVENT INVENTOR 1::4 HERBERT PAGROLL BY W QR ATTORNEYS United States Patent 3,098,034 FRACTIONATION 0F OILS BY SELECTIVE EXTRACTION Herbert P. A. Groll, Kyrkogatan 1A, Molndal, Sweden Filed Aug. 23, 1954, Ser. No. 451,566 Claims priority, application Sweden Aug. 24, 1953 Claims. (Cl. 208316) This invention pertains to a fractionating method comprising liquid-liquid extraction. The materials which can be fractionated according to my invention for the pur pose of improving same by refining and/or separating them into a plurality of useful constituents are oils and other organic substances of relatively high molecular weight, but are soluble in at least one of the solvents to be enumerated later and comprise a large number of substances, some of which are enumerated as follows: petroleum, its higher fractions and distillation residues, such as topped crudes, and especially, short residues, as well as tar oils, shale oils, and synthetic hydrocarbon oils such as Fischer-Tropsch products, products of coal hydrogenation, and products obtained by polymerizing hydrocarbons and certain substituted hydrocarbons. A further group of materials which can with special advantage be fractionated according to my invention comprises natural fats and oils of animal and vegetable origin, i.e. glycerides, fatty acids and mixtures of these substances with natural resins and resinic acids e.g. crude talloil or talloil fatty acids as well as crude mixtures of fatty acids such as may be obtained by refining of fats and oils, by hydrolyzing fats and oils, and by oxidation of paraflin wax. Other mixtures suitable for being fractionated according to my invention are essential oils, terpenes, rosins, rosin oils etc. as well as polymerized oils and soluble types of artificial resins e.g. standoils, boiled linseed oils, alkyd resins, modified alkyds, polyester resins, and certain modified epoxy and phenol resins, polyvinyl esters and ethers, polyacrylates and methacrylates and various kinds of co-polymers.

It is an object of this invention to provide a method for fractionating of oils by selectively extracting them in a plurality of fractionating stages with preprepared liquid solvents consisting of at least two components of which at least one is a liquid under the operating conditions, while another one is a gas not liquifiable at the temperature of the extraction but dissolved in said liquid, the percentage of said dissolved gas being dilferent in every extraction stage. By the presence of dissolved permanent gas the solvent is modified with respect to its solvent powder. Thus modified solvent possesses a lower solvent power for high molecular oil constituents than the pure solvent, free from dissolved gas.

Another object of my invention is to provide a simple and effective method for recovering both the extracted portion of the oil and the bulk of the solvent from the extract and simultaneously, or by a simple modifying step following said recovery, adjust the composition of the solvent for use in another extraction stage.

An object of a specially useful modification of my invention is to operate the above described process continuously in such a manner that the solvent flows in countercurrent essentially through the whole plant i.e. from stage to stage in the opposite direction to the flow of the oil to be fractionated. Thus a very essential advantage is gained by the fact that such minor amounts of dissolved oil, as many fail to be recovered, are carried over to that stage in which, owing to the countercurrent principle, they will least interfere with the fractionating effect desired.

An object of a still further useful modification of my invention is to operate at least one of the extraction stages of the process described continuously in a long extended column, in which the degree of modification of the solvent, i.e. its content of dissolved permanent gas, is adjusted so that two liquid phases i.e. extract and residue are formed and the various constituents of the oil are divided into two fractions of which one is dissolved in the extract and the other in the residue. Said phases move by the influence of gravitation within the column to its opposite ends. Thereby that exchange of matter is achieved, which is considered most essential for an efii cient fractionating effect, and the thus fractionated phases are accumulated and clarified at the opposite ends of the column wherefrom they are withdrawn.

One of the features of my invention, essential for achieving the objects mentioned, comprises removal of the oil fraction from the extract and the change of the degree of modification, i.e. the content of dissolved gas in the solvent, between every extraction stage and the next one. This I accomplish by subjecting the extract, after separating it from the extraction residue, to an increase of the saturation pressure of the dissolved gas. I may increase the saturation pressure either by pressing more gas into the extract and/or by increasing the temperature of the extract. Both these measures cause a rise of the saturation pressure and a subsequent precipitation of all or part of the oil fraction from the extract. After allowing the precipitated phase to settle I withdraw it from the (in most cases supernatant) solvent phase. If the latter has been liberated from the oil by pressing in more gas, the solvent thus recovered has achieved a higher degree of modification and may thus directly be used for extracting the oil in an extraction stage requiring such higher degree of modification.

If on the other hand a lower degree of modification is required of the solvent in the next extraction stage I prefer not to introduce any additional gas which would have to be removed again but to increase the temperature of the extract. This will increase the saturation pressure sufiiciently for precipitating part or all of the oil constituents dissolved. After withdrawing the precipitated phase the solvent thus regenerated will, if cooled down to the same temperature which it had before it had been heated, reassume the same degree of modification as it had before. In order to decrease the degree of modification I strip some of the gas from the liquid. This may be done at the operating temperature or at an increased temperature. I usually prefer to strip the gas at an increased temperature because this enables me to recover the gas at a higher pressure, preferably so high as to obviate recompression for re-use. In order to adjust the modification of the solvent mixture for the next extraction stage I strip only enough gas from the liquid that the saturation pressure of the solvent after cooling down to operating temperature becomes that required for said next extraction stage.

The term saturation pressure which I use in this specification should be interpreted only as a convenient way of expressing the physical condition of the solventgas pair at any point .of the system. The saturation pressure is dependent upon the amount of gas dissolved in the solvent as well as on the temperature. It can be determined very easily by withdrawing a sample of the solvent from the apparatus through a sampling valve into a small pressure sampling vessel, the latter being provided with a pressure gauge and a vent valve. The vent valve is closed so that the pressure between the apparatus and the sampling vessel is completely equalized, and the sampling vessel is completely filled with liquid. Then the sampling valve is closed and the vent valve is carefully opened for just a short moment so that only a very small amount of liquid and gas is withdrawn. As soon as the vent valve is closed again the pressure gauge will show a constant pressure which is the saturation pressure.

I wish to emphasize in this connection that the saturation pressures which in the following examples and in the figures attached to this specification are designated with p1, p2, p3, etc. are not at all identical with the operating pressures occurring in the different apparatus of the plant. These operating pressures must be at least as high as the saturation pressures otherwise the gas would escape from the solvent. In most cases I prefer considerably higher operating pressures for practical reasons for instance for being able to pump the solutions without gas lock. In this case the system becomes completely full of liquid, so that the operating pressure becomes the hydraulic pressure of the liquid.

In order to make various other terms used in the following specification and in the ensuing claims more clear and in order to simplify the language and to avoid unnecessary repetitions I am giving below a definition of such terms as may need explanation:

Oil=the material to be extracted. The term is meant to include all mixtures of soluble oleaginous or resinous matter, liquid as well as solid, natural as well as synthetic, which according to the definition given at the beginning of the description can be fractionated by applying my invention. The term oil is further meant to include those fractions or cuts obtained by fractionat-ing the original oil but which still contain a plurality of oil constituents and which therefore, are, if desired, to be fractionated further by the process of my invention.

Unmodified solvent=a solvent consisting of one or more compounds of relatively low molecular weight all of which are liquid at the temperature and pressure of operation.

Modifier=a gas comprising at least one compound whose critical temperature is below the operating temperature and which when dissolved in the unmodified solvent decreases the solvent power of said solvent for the oil.

Modified solvent or solvent mixture=synonyms for the homogeneous liquid mixture consisting of the unmodified solvent and the gaseous modifier dissolved therein. When recovered by precipitation the modified solvent may contain varying amounts of the oil fraction carried over from the previous fractionating stage.

Extract the solution of one or more of the more soluble constituents of the oil in an excess of modified solvent obtained and withdrawn as the one of the two liquid phases during a fractionating stage.

Residue=the extraction residue obtained as the other liquid phase in and withdrawn from any fractionating stage of the process. It consists of one or more of the lms soluble oil constituents together with a certain amount of solvent mixture which according to the laws of equilibrium phase distribution is dissolved in said other liquid phase.

Precipitate=the phase, rich in oil constituents, which is precipitated from the extract by pressurizing it with the gaseous modifier and/or by heating it. It is then withdrawn for further use and like the residue contains a certain amount of dissolved solvent mixture.

Cut:any residue or precipitate still containing solvent mixture and withdrawn for further treatment in another stage or for recovery of the fraction of the oil contained therein.

Fraction the oil constituent or mixture of constituents of any cut after the solvent components contained therein have been removed. The fractions are thus the products obtained in the process according to my invention.

The term Fraction is however generically used in the claims to describe a portion of the oil constituents or mixture separated from another portion whether the same still contains solvent or not.

The choice of the liquid unmodified solvent and of the modifying gas depends wholly upon the nature of the oil to be treated. Thus a combination of propane and methane is especially suitable for treating a mixture of free fatty acids. In this case methane pressures between 50 and atmospheres are suflicient for modifying the solvent for the different fractionating stages. If pentane and methane were used instead for fractionating the same type of fatty acids, pressures as high as l50200 atmospheres would become necessary so that a much heavier type of apparatus would have to be used.

On the other hand, I have found it to be practically impossible to fractionate higher molecular condensation products such as alkyds with propane as solvent because these artificial resins are completely insoluble in propane. Even pentane may be quite unsuitable as solvent for such high molecular compounds. In order to get such compounds in solution I prefer to use an unmodified solvent with a higher solvent power. I may increase the solvent power of the solvent by using a higher molecular homologue or by admixing an auxiliary solvent whose chemical nature may be different from that of the solvent which is to be modified by addition of gas.

Suitable auxiliary solvents are white spirit, toluene, benzene, chlorinated hydrocarbons, alcohols, esters, ketones etc. Certain high molecular oils such as artificial resins should, however, be dissolved too slowly in any of the solvents which can be modified by pressurizing with gas. Therefore I prefer to dissolve these high molecular oils first in the pure auxiliary solvent. If necessary, I may remove impurities from this preliminary solution by filtration or the like. Most of the suitable auxiliary solvents have such a high solvent power that they could not be used themselves as unmodified solvent because they are not at all or only at excessive pressures modifiable.

In order to proceed with the fractionation according to my invention I may therefore dilute the preliminary solution in the auxiliary solvent with an unmodified solvent of the class, which can be modified by pressurizing with gas, for instance with a suitable paraffin hydrocarbon. I choose the nature of the modifiable solvent and its proportion to the auxiliary solvent so that on the one side the oil to be fractionated is completely soluble in the mixture before it enters the fractionating stage. On the other side I prefer to let the concentration of the solvents in the mixture, which is to be introduced for being extracted, not essentially exceed that in the residue and/ or precipitate formed during the fnactionating process.

Instead of diluting the preliminary solution of oil with some unmodified solvent before extracting it, I may introduce the preliminary solution directly into the first fractionating stage where it in contact with the modified solvent soon comes into an equilibrium phase condition with the modified solvent by forming extract and residue in the manner described above.

Consequently a certain part of the modified solvent mixture is dissolved in the residue as well as a certain part of the auxiliary solvent is dissolved in the extract thus diluting the modified solvent. The resulting solvent blend possesses several advantages. Among others it has a sufiicient solvent power for those constituents of the oil which have to be extracted, and the auxiliary solvent contained therein is automatically accumulated to a certain extent in the precipitates as Well as in the fractionating residues. In many cases it suffices therefore to collect the solvent distillate from the cuts in a separate receiver. The question as to whether the thus recovered distillate can as such be re-used as auxiliary solvent or whether it must be refractionated must be decided upon the merits of the case in question.

In certain cases I found it suitable to apply other organic and/or inorganic compounds as unmodified solvents or modifying gas respectively. Thus, I may use ethane or a mixture of methane and ethane as gaseous modifier or I may operate the process at a temperature above the critical temperature of propane and use a gasoline cut as unmodified solvent and propane as gaseous modifier. Suitable other pairs of unmodified solvent and of gaseous modifier are for instance liquid carbon dioxide and nitrogen, carbon dioxide and nitrous oxide, dichlo-romethane and nitrous oxide, difluoro dichloromethane and methane, dilluoro-dichloromethane and nitrous oxide, sulphur dioxide and nitrous oxide etc.

7 I may regulate the amount of gaseous modifier dissolved in the liquid either by pressing a measured amount of gas into a measured amount of liquid or by passing the gas flowing at a certain measured rate into a stream of the liquid solvent which also flows at a certain measure rate through a mixing device, or by saturating the liquid with the gas under a certain constant pressure.

When I am carrying out the continuous process according to my invention in the aforementioned modification with at least one fractionating column, said column may be an unpacked tower or it may contain baffles or other devices which are suitable for dispersing the feed and the reflux and for enhancing the contact between the oil and the solvent or the extract respectively. I prefer to use such devices especially with larger column diameters in order to counteract convection turbulence which occurs especially easily in wide columns and which should frustrate the countercurrent effect. As suitable devices I may use bafiles or plates or I may fill the tower with rings or other packing material or I may provide it with a coaxial spiral of wire gauze. In certain cases I may use a column provided with alternating packed zones and zones in which mechanical spreading or mixing devices such as stirrers are arranged.

If my invention is carried out in columns I prefer to pump the oil into the middle of the column. From this point the oil falls in finely divided form through the modified solvent which is pumped in at the bottom of the column. Thus in the lower part of the column, i.e. in the extraction zone, the oil is selectively extracted by the intimate contact with the modified solvent. 'Ihis selective extraction comprises partial solution followed by a gradual exchange of matter between the two phases. As a result of both these phenomena the various components of the oil are distributed between the two liquid phases which are allowed to separate after they have been subjected to the effective countercurrent contact in the extraction zone referred to above. The two phases leave the extraction zone in the two opposite directions.

Normally the heavier phase is the extraction residue which contains relatively little solvent dissolved in the less soluble oil fraction. This fraction may of course be a mixture of several constituents of the oil. The residue is withdrawn from the bottom of the column and either is passed on to the next column for refractionating or it may be taken out as a cut and treated in any desired manner. Thus, the residue may be liberated iirom the gaseous modifier which it contains and the resulting solution may be refined or bleached chemically or with adsorbents, or certain components may be separated by fireezing out or low temperature crystallization respectively. In this case, -I may use the heat of evaporation of part of the solvent as means for cooling down the rest of the solution, so that crystallization of those components which have a relatively high melting point takes place. Eventually the oil fraction contained in the residue is recovered by distilling off the solvent which is dissolved therein.

The extract normally is the lighter phase. It consists of a relatively large amount of modified solvent together with those constituents of the oil which have been dissolved according to the degree of modification which the solvent had been subjected to by the addition of gas. The extract rises to the upper part of the column where is meets a reflux of oil. In this upper part of the column a similar exchange of matter takes place between the two liquid phases as in the lower part. This exchange causes a rectification of the extract.

The details of the process described above are valid if the oil is heavier than the solvent. If in special cases the solvent is heavier than the oil only the direction of flow in the tower is changed, i.e. the residue rises up in the tower instead of falling down while the extract falls down. Consequently, the points of entrance and withdrawal of the solvent, the reflux, and the residue are changed according to requirements.

For obtaining a reflux which is desirable for continuous fractionation in order to rectify the extract, I may operate the column at a sufliciently high pressure or I may prefer to bring the extract to a higher operating pressure e.g. by means of a pump. Simultaneously with/or after the increase of the operating pressure I increase the saturation pressure of the modifying gas either by pressing in more gas, or by increasing the temperature, or by a combination of both these procedures. By the increase of the saturation pressure the solvent is further modified so that the oil which had been dissolved in the extract is wholly or partially precipitated from the solution.

However, the precipitate thus obtained does not only consist of components of the oil but just like the extraction residue described above it is a solution of a minor part of the modified solvent in the oil, thus it contains for instance propane and some dissolved methane. In most cases when I have used the combination of methane and propane I have found that the precipitates and the extraction residues obtained at the various points of the plant contained between 25 and 60% by weight of modified solvent. The solvent content may however change quite appreciably according to the nature of the oil and that of the solvents. Considerable changes may likewise be caused by changing the physical conditions under which the fractionation takes place. Such conditions are among others, temperature, pressure, proportion of solvent to oil, reflux ratio etc.

A certain part of the precipitate obtained in the manner described above I pass as reflux back into the column. The rest of the precipitate may either be withdrawn as a cut in order to recover the oil fraction contained therein by distilling off the solvent or I may pass the out directly to another iractionating column in order to separate it into two additional cuts.

The solvent which had been liberated of all or most of the oil by the precipitation described has, if the saturation pressure had been increased by pressurizing with more .gaseous modifier, obtained a higher degree of modification. I prefer to use this higher modified solvent directly in the next stage of the tractionating process ie in a column which is operated at a higher degree of modification. However, I may also operate the next column at a lower degree of modification. In this case I achieve the above mentioned increase of the saturation pressure and the ensuing precipitation by increasing the temperature. After liberating the solvent from the precipitate formed I may drive off part of the modifying gas in a stripper and then cool down the solvent to the operating temperature of the next column. In this way, I can decrease the degree of modification of the solvent for use in the next column.

It is known that an increase of the hydraulic pressure of a solvent or of a solvent mixture of the kind which I am using in carrying out my invention can increase the solvent power of the solvent. It has been suggested to utilize this effect for a specially accurate control of the solvent power in connection with regulating the fractionation in extraction columns. My invention does not at all depend upon this effect, which, on the contrary, is diametrically opposed to the eflect of adjusting the degree of modification of the solvent by pressurizing it with a gaseous modifier. On the other hand the known hydraulic pressure elfect referred to above may be used in a plant built for carrying out the process according to my invention as a means of additional regulation of the solvent power.

The operating temperature does not play any decisive part in the fractionating process according to my invention. I therefore prefer to operate the fractionating stages at room temperature or at a temperature most economical with respect to the temperature of the cooling water available at the plant site. For obvious reasons the operating temperature should be at least so much above the temperature of the cooling water that the heat exchangers for cooling the modified solvent down to the operating temperature do not need to have an inconveniently large tube surface. In certain cases I choose the operating temperature according to the physical properties of the oil and of the cuts obtained. Thus, the temperature should always he kept high enough for avoiding the separation of any solid matter from the cuts which might plug lines or valves.

The proportion of oil or its concentrated preliminary solution to the solvent which I use for extraction can vary within very wide limits according to the nature of the oil, the solvent, and the modifier, to the operating conditions, and to the type of apparatus used. I prefer to use more solvent than oil. Feed proportions by volume between the solvent and the oil may thus be chosen between three to one and about fifty to one. For the batch process I usually choose proportions between 3/1 and 10/ 1. For proportions considerably larger than 10/1 a batch apparatus would become inconveniently large and the margin between the oil content of the extract and that part thereof which can no longer be precipitated becomes too small for practical operation. If I use a continuous operation without reflux the proportions between the rate of flow of the solvent and that of the oil can be somewhat higher but the last named margin is the limiting factor for this method too. T he question of proportions to be used becomes, however, quite different when continuous operation with reflux is applied. In this case the reflux ratio and the feed proportion are dependent on each other. I choose the reflux ratio according to the desired fractionating effect in exactly the same manner as is usual with fractional distillation. If a high reflux ratio is used the oil components in question soon accumulate in the content of the column. Gradually a flow equilibrium is reached between the various constituents and the phases present in the column. This equilibrium obviously depends upon the chosen feed proportions and the likewise chosen reflux ratio. It is quite obvious therefore that if the feed ratio between the solvent and the oil is too low in comparison to the reflux ratio, the oil concentration in the column becomes so high that it soon will enter a location on the solubility diagram in which no longer any precipitation can occur, simply because the content of the whole column approaches a composition which is the same as that of the extraction residue or of the precipitate respectively. Therefore, I may well use feed proportions of 50/1 if I simultaneously use high reflux ratios e.g. 5/1 or /1. If I desire to fractionate the oil within very narrow limits of fractionation e.g. when separating certain vitamin fractions from fatty oils I may use still higher reflux ratios than those mentioned above and I shall then increase the feed ratio accordingly.

Although the principle of my invention is comparatively simple, a continuous fractionating plant designed according to any invention becomes rather complicated. Furthermore there are several important modifications of a flow diagram which may be chosen according to the nature of the oils and the fractions desired. Of the examples described below No. 1 shows the batch process while Nos. 2-5 together with FIGURES 1-4 show various modifications of the continuous process. In the examples petroleum ether containing chiefly pentanes, and propanepropylene, have been used as unmodified solvents and methane as modifying gas. It is to be understood that I do not intend to limit my invention to the use of these solvent combinations.

EXAMPLE 1 In a horizontal stirring autoclave 3200 mls. of petroleum ether was saturated with methane under a pressure of 164 atmospheres. Into this solvent mixture 750 mls. of boiled linseed oil with an acid number of 8 was pumped. This content of the autoclave was violently stirred during a few minutes. Then the autoclave was put in an inclined position so that the heavier phase which separated rapidly could be drained off quantitatively. This lower layer, amounting to 1250 mls. after the methane dissolved therein had been allowed to escape, consisted of about 60% of oil and about 40% of petroleum ether. This extraction residue was put aside for further treatment. The extract which had remained in the autoclave was also withdrawn, and by evaporating the solvent mixture from this extract, 60 mls. of an oil fraction I was recovered. This-fraction was very dark and had an acid number of 20.

The autoclave was filled with fresh petroleum ether which was saturated with methane under a pressure of 145 atmospheres. The extraction residue from the first fractionating stage was pumped into the autoclave and agitated and separated in the same manner as described for the first fractionating stage. The lower layer was again withdrawn and put aside for further treatment. The evaporation of the total amount of the solvent mixture from the extract, as it had been done in the first fractionating stage, appeared inconvenient and quite time consuming. Therefore this second extract, which had remained in the autoclave, was not withdrawn but was instead heated to the temperature of about 60 C. so that the pressure rose to 230 atmospheres. By this increase of the saturation pressure the larger part of the oil present in the extract was precipitated and could be withdrawn as a lower layer amounting to 230 mls. after the methane had been allowed to escape. By evaporating all of the mixed solvent from this residue a fraction II amounting to mls. was obtained. This fraction was very light colored and of comparatively low viscosity. It had an acid number of 6. The autoclave in which the solvent mixture had remained was cooled down to room temperature and some methane was pressed in, so that the saturation pressure amounted to atmospheres. The second extraction residue mentioned above was pumped back into the autoclave and treated in the same ways as described above. The new residue which was withdrawn from this third fractionating stage amounted only to cm. and was very dark and cloudy. After the solvent mixture had been removed from this residue about 100 cm. of a fraction V remained. This fraction had an acid number of 5.6 and was highly viscous. The extract which had remained in the autoclave was precipitated by heating it to 60 C. so that the pressure rose to 200 atmospheres. The precipitate amounted to 300 em. after evaporation of the solvent and was designated as fraction III. As it appeared unnecessary to proceed with further fractionation the whole extract was removed from the autoclave and the solvent mixture distilled otf. The distillation residue which was designated as fraction IV had an acid number of 5 and was very light colored. The fractions Ill and IV represented the main part of the boiled linseed oil. They were investigated further and it was shown that they were extremely stable when a drier had been added, i.e. the drier did not at all show such a tendency to be precipitated as can frequently be observed with boiled linseed oils.

EXAMPLE 2 In FIGURE 1 the oil is pumped by pump M from tank 1 and propane from tank 2 to a mixer 3. Only so much propane is required that the solution becomes sufliciently mobile. I prefer, however, to add as much propane here, as is necessary to replace all the propane withdrawn with the cuts F1F5 from the plant. Should, for reasons discussed later, a further amount of propane be distilled from the evaporator 43, I may replenish this amount too by mixing it with the feed or by pumping it with the pump 47 to the mixer 48 where it may be modified for use in the recycle line 330. The mixture passes to the separator 4 in which heavy impurities can settle out. If it is necessary the mixture can be filtered through the filters which are used alternatively. A surge tank 6 equalizes the unevenness of the filtered stream which is caused by the changing flow resistance of the filter. (In such cases in which the oil is sufficiently pure it is not necessary to pretreat it in this manner and the apparatus 3-6 can partly on wholly be dispensed with.)

The solution or the oil respectively is pumped by the pump 7 into the mixer 8 to which a sufficient amount of methane is admitted that the liquid mixture assumes the highest saturation pressure P4 used in the plant. The oil thus saturated with methane meets a flow of modified solvent rising in column 9. The solvent power of the modified solvent has been reduced by addition of methane so that it posses the same high saturation pressure P4 as the feed. The modified solvent extracts from the oil under counter-current its most soluble constituents erg. the lightest or the least polar molecules and takes them along to the top of the column. From the top the extract is pumped with pump 10 to a still higher operating pressure and is heated up in the heater 11. By the rise of temperature the saturation pressure of the extract rises to a value which is, however, still below the new operating pressure. As a result nearly all the oil which had been dissolved is precipitated and separated in the separator 12 and after cooling in the cooler 13 it can be drawn oil through the valve 14 as cut P1. In order to increase the fractionation effect in column 9 as much as possible, not the whole cut is withdrawn but its larger part is recirculated through the valve 15 to the upper part of the column so that the reflux meets the flow of rising extract. In this way the fraction of oil which had been dissolved in the solvent is rectified.

The modified solvent which forms the upper layer in the separator 12 is in general sufliciently pure to be recirculated to the last column Ztlb in the system. Before this is done the excess of methane dissolved is stripped off in the methane stripper 17.

That part of the oil which is not dissolved in column 9 dissolves a certain amount of solvent, thus forming the residue which is collected as the lower layer in the bottom of the column and passes through the line 18 and valve 10 to column 20. The whole fractionating and precipitating equipment comprising column 9 and its accessories 1017 represents one type of fractionating unit which hereinafter is referred to as fractionating unit A. In column 20 the procedure described for column 9 is repeated with 2 diiferenees:

(a) The degree of modification expressed by the saturation pressure P3 is lower; the solvent in column 20 contains a smaller amount of methane than that in column 9 and its solvent power is considerably increased. The solvent therefore dissolves a fraction of less soluble oil constituents.

(is) The precipitation of the dissolved fraction from the extract is achieved by dissolving more methane in the extract instead of heating it.

For this purpose the extract is pumped from the top of the column 20 with the pump 21 to the mixer 22. There a sufficient amount of methane is admitted so that the saturation pressure rises, preferably to P4 so that the modified solvent after separation from the cut F2 in the separator 28 can be passed on to the bottom of tower 9 with the right degree of modification. The methane passes from the methane tank 23 through valve 24 into the saturator 2. The methane tank is kept at such a gas pressure as is necessary for passing the :gas with a sufliciently high flow rate to the saturators 8, 22 etc. The methane is compressed up to the pressure necessary by the compressor 25 but normally is recirculated to tank 23 from the gas stripper 17 through the dephlegator 26 and the line 27. In the mixer 22 the greatest part of the oil fraction which has been dissolved in column 20 is precipitated from the extract. The emulsion formed by this precipitation flows to the separator 28. The precipitate which separates there is withdrawn through the valve 29 as at P The larger part of the precipitate is, however, refluxed through valve 30 to the upper part of the fractionating column 20. This reflux causes a rectification in the same way as described for column 9. The column 20 and all its accessories 2030 form a type of fractionating unit hereinafter called fractionating unit B.

The residue from the extraction zone of the column 20 is withdrawn and passes on to column 200 where the fractionating procedure described for tractionating unit B is carried out once again and can be repeated in additional fractionating units B as often as is necessary for obtaining the desired number of fractions. The height of the columns and the reflux ratios necessary in the different columns are determined or calculated according to known principles in a manner analogous to the calculation of fractionating operations by distillation.

As has been described above the solvent mixture, after having been liberated of some of its methane content can be recirculated directly for re-use in the last column 20b. For this purpose the solvent is cooled in the cooler 31 down to the extraction temperature of the plant and is expanded through the valve 32 into the line 33c. It enters the bottom of column 2% through the valve 340.

The solvent flows through the entire plant in countercurrent relationship to the oil. After extraction of the extract in the saturators 22b, 22a, and 22, it separates as an upper layer in the separators 28b, 28a, and 28, respectively. These upper layers are passed through the lines 33b, 33a, and 33, and the valves 34b, 34a, and 34, respectively, into the bottom portions of the next tower, where they serve as solvents for the fractionation therein as described.

It is possible that the oil to be treated contains certain very soluble constituents which should accumulate in the circulating solvent mixture. The danger of such an accumulation is particularly great if the compounds which remain in the solvent mixture after separti'on in the separator 12 have a lower molecular Weight than those constituting the fraction F In that case and generally if it is desired to recover a certain amount of pure unmodified solvent I prefer to pass a certain part of the solvent mixture through the line 35 and the valve 36 to the heater 37 and the gas stripper 38 which differs from the stripper 17 only by being operated under a lower pressure. If I use propane as a solvent the pressure should, however, be sufficiently high that a reflux of liquid propane in the dephlegmator 39 is obtained with ordinary cooling water without the necessity 'of refrigeration. The methane which leaves the condenser 39 is compressed 'to the pressure of the methane tank 23 by the compressor 25. The completely stabilized propane solution flows through line 40 and the valve 41 into the heater 42 and is evaporated in the evaporator 43. The vapors are condensed in the cooler 44 and are recirculated to the propane tank 2. The distillation residue which remains in the stripper 43 is cooled down in the cooler 45 and is withdrawn through the valve 45 as a fraction F The cuts F F contain, as has been explained above, certain amounts of propane and methane in phase equilib rium with the extract or the recovered solvent mixture respectively. All these fractions I collect in separate closed surge tanks. I may subject all or some of these cuts to refining and/or dewaxing treatments which I have de scribed in the specification. For this purpose I may first 'degas them, but I prefer to treat them before I remove all of the propane, because most treatments can be carried out more conveniently with the less viscous solutions than with the concentrated oil fractions. Eventually, all cuts which do not have to be refractionated or otherwise used in solution are subjected to stripping operations in apparatus of conventional design for recovering the solvent and returning its liquid components to the tank 2 and the gaseous modifier to the tank 23. I do not show this auxiliary plant in the drawings of this patent application because this would unnecessarily complicate them. The propane and the methane recovered as described is primarily used for prediluting the oil feed as described in the beginning of this example.

EXAMPLE 3 In many cases I found it necessary to operate the system shown in FIGURE 1 with so small differences in the degree of modification between two columns following each other that the amounts of methane, which I had to add to the mixers 22, 22a or 22b for precipitating the extract, were so high that I could not use this solvent, highly pressurized with methane, in the column 9 or 20 or 28 because the degree of modification required had been exceeded very much. I could of course correct this overmodification simply by allowing the excessive methane to escape. This can be done for instance by providing the lines 33, 33a and 33b with a simple expansion chamber with an expansion valve. Such an arrangement would, however, not only be uneconomical but it would also make the operation of the plant considerably more diflicult. Therefore I prefer in such cases, as defined above, to precipitate the extract by a combination of heating and pressurizing with gas. This method is shown in FIG- URE 2 for one column only. Obviously this method is equally suitable for all such cases etg. in FIGURE 1 for all columns with exception of column 9.

The oil entering from line 118 through the valve 119 is extracted in the column 120 with the suitably modified solvent, which enters through the line 133a and the valve 134a. The extract is pumped from the head of the column with the pump 121 through the pre-heater 111 to the mixer 122. In the pre-heater 111 the extract is heated so high that a sufficiently large part of the dissolved oil is precipitated. Through the valve 124 methane is admitted at an accurately determined rate which is adjusted so that the solvent mixture after it has been cooled down in the cooler 131 will assume just the right degree of modification for use in the column 109. It is easily seen that I obtain in this case a complete precipitation of the cut from the extract without having to apply an excessive amount of methane. The extract treated in the manner just described passes on to the separator 128 where the precipitate settles out. The precipitate is cooled down in the cooler 113 to the operating temperature of the column 120. Part of it is returned as reflux through the valve 130. The rest of the precipitate is withdrawn through the valve 129 as cut F from which the oil fraction contained therein may be recovered by distilling off the sol vent mixture. The upper layer from the separator 12% is cooled down in the cooler 131 to the operating temperature of the column 109 and is passed to this column by the line 133 and the valve 134. The fractionating equipment consisting of the column 120 with all the accessories-described in the foregoing example will in following be referred to as fractionating unit C.

EXAMPLE 4 In many cases it is undesirable that the heavy residue contained in the oil follows with the oil through the whole fractionating plant for eventually being withdrawn as fraction F from the bottom of column b. This can, however, not be avoided if a plant laid :out according to the flow diagram shown in FIGURE 1 is used. In the certain cases referred to it is therefore better to use another flow diagram which is shown in FIGURE 3. The fractionation method shown in this figure differs from that shown in FIGURE 1 by the fact that the cuts F to F are withdrawn from the bottoms of the respective columns instead of from the separators at the top and by the fact that the fractionation is carried out with degrees of modification which are increased from column to column. The optional pretreatment of the oil is the same as in Example 2 and it is therefore unnecessary to describe it again. From the mixer 53 in which the oil, or the oil containing some unmodified solvent or some auxiliary solvent respectively, is pressurized with methane from tank 73 through the valve 160 until it acquires a saturation pressure which is in equilibrium with the modified solvent in column 59. It enters the middle zone of the column 5 9 which is equipped as fractionating unit B and is extracted with a solvent mixture consisting of propane with a moderate amount of methane. This solvent mixture enters the column through the line 83 and the valve 8 and dissolves a major part of the oil so that only a minor part of residue is withdrawn through valve as out F The extract is pumped from the top of the column S9 with the aid of the pump 71 to the mixer 72 in which the oil fraction dissolved in the extract is precipitated by pressurizing with more methane which enters the mixture through the valve 74 from the tank 73. The rate of methane addition or the new degree of modification respectively is adjusted so that on the one side it suffices for precipitating the oil from the extract and on the other side the degree of modification of the solvent mixture is sufiiciently increased so that it can directly be used as modified solvent in the column 70b which is operated with a degree of modification of the solvent mixture expressed by the saturation pressure P The precipitate is separated in the separator 78 and part of it is refluxed through the valve 7% to the column 59, while the rest of the precipitate is passed on to the column 70. The upper phase from the separator 78 is recirculated through the line 330 and the valve 840 as highly modified solvent to the last column 70b. In the same manner as has been described in Example 2 a certain part of the solvent may, if this is deemed necessary, be deviated through the valve 86 to devices for stripping off the gaseous modifier and for recovery of the propane by distillation. These devices are of precisely the same type as those shown in FIGURE 1 and are therefore not shown in FIGURE 3. The precipitate which passes through the line 68 enters the column 70 through the valve 69. In this column which is equipped as fractionating unit A the precipitate meets a stream of solvent mixture with a higher degree of modification, corresponding to a saturation pressure P This solvent mixture has a lower solvent power than that used in column 59 so that not all of the precipitate will be re-dissolved. The undissolved residue is Withdrawn from the column 70 through the valve 80:: as cut F The extract is rectified in counter-current to the reflux and is pumped from the head of column 70 by the pump 60 into the heater 61. By the temperature rise the oil is precipitated from the extract. This precipitate is separated in the separator 62 and is cooled in the cooler 63 to the operating temperature. Part of the precipitate is refluxed through the valve 65 to the column 70. The rest of the precipitate passes through the line 68a and the valve 6% to the column 70a Where the procedure just described is repeated. The solvent mixture which has been liberated from the precipitate in the separator 62 passes through the valve 66 to the stripper 67 where part of the methane is stripped off through the dephlegrnator 76 and the line 77 to the tank 73. The residual solvent mixture is cooled in the cooler 81 and passes to the column 59 through the valve 84 and the line 83. This solvent mixture has now acquired the comparatively low degree of modification which corresponds to the saturating pressure P The manner of operation of the further columns 70a and 70b is completely analogous to that described for column 70 with the only diiference that the saturation pressure P is higher than P and P higher than P I may provide after the column 70b still further columns if I desire to obtain a larger number of cuts. The lightest fraction obtainable in the plant according to FIGURE 3 is contained in cut F which is withdrawn from the precipitate from the extract of column 70b through the valve 690.

13 EXAMPLE In certain cases it is preferable to separate the oil first into two main fractions both or which are refractionated. A system suitable for this type of operation is shown in FIGURE 4. The oil which may contain some solvent and/or auxiliary solvent is pretreated and presaturated with methane in the same manner as described in Example 2. The devices provided for this purpose are not shown again in FIGURE 4. The oil is passed through the line 201 into a fractionatin-g unit C which may, however, even be laid out as fractionating unit A for B depending upon the question in which part of the apparatus the larger part of the solvent mixture, which is recovered from the extract at the headiof the fractionating unit in question, is to be re-used. In the plant shown partly in FIGURE 4 I had chosen a fractionating unit C, because this possesses the higest flexibility. The cut precipitated from the extract i.e. the overhead cut of the unit C passes from the separator 222 through the cooler 213, the line 229 and the valve 230 to the column of a fractionating unit A. In this fractionating unit A the cut is separated into two further cuts which are withdrawn as residue from the bottom and as precipitate from the top. One or both of these cuts may be refractionated in further units. In the plant shown in FIGURE 4 the extraction residue from the bottom of the unit A is withdrawn as cut F in order to recover the oil fraction therein. Only the precipitate recovered from the extract i.e. the overhead out of the unit A is refractionated in a further unit A. The bottom out from the unit C passes through the line 218 and the valve 219 into the column of a fracti onating unit B Where it is separated into two further cuts. Whether one of these further cuts and if so, which one should be fractionated further, depends upon the nature of the oil which has to be fractionated as well as upon the specification of the fractions desired. In general I prefer to use a fractionating unit of the type B or C for refractionating a bottom cut. Likewise I prefer to use type A for refractionating a top out.

The following table shows solvent mixtures which I have used in firactionating various types of oil, fatty acids, and artificial resin and the degrees of modification expressed as saturation pressures which I used in the various fractionating stages:

Saturating Pressures Applied in the Fractionation of Fatty and Resinous Matter Methane saturation pressure, kg./cm. Material Solvent mixture P1 P2 Pa P4 P5 P0 Warmpressed Petroleumether. 155 160 175 linseed oil.

Do PIiODaDG-PZ'ODY- 40 56 75 one. Low grade lin- Petroleumether- 138 140 148 160 seed oil. 138 150 155 157.5 180 Boiledlinseedoih do 140 155 160 170 Stand oil viscosdo.

ity of 5000 0S. Alkyd typeA- White spirit 22 25 30 35 petroleum ether. Alkyd typeB do 56 60 65 75 Herringoil Petroleumether. 152 160 170 185 Soyat'attyacids do 174 176 178 181 Coconut fatty d0 210 212 216 220 acids. Crude ta1loi1 d0 185 Do Prlopane-ptopy- 30 60 70 94 ene. Fatty acids ob- Petroleumether. 170 172 174 185 tained by hydrolyzing linseed oil.

I claim:

1. Method for the fractionation of high molecular weight organic material which comprises intimately contasting the organic material to be fractionated in a fractionating step with a liquid solvent containing a pre determined amount of a dissolved gas which decreases its solvent power to thereby selectively extract a fraction of said material, removing the solvent with the extracted fraction dissolved therein, separating at least a portion of the extracted fraction from the solvent, contacting at least one of the extracted fractions and the extraction residue with the liquid solvent containing a diiferent predetermined quantity of dissolved gas in at least one further fractionating step to thereby selectively extract a further traction of said material, removing the solvent with the further extracted fraction dissolved therein and separating at least a portion of the extracted fraction from the solvent.

2. Method according to claim '1, in which said contacting in said further firactionating step is effected with said extracted fraction, and in which the extraction residue is recovered.

3. Method according to claim 2, in which said contacting is effected by passing the organic material and solvent in countercurrent flow contact.

4. Method according to claim 1, in which the solvent in each fractionating step contains a greater quantity of said dissolved :gas than the solvent in the next subsequent firactionating step.

'5. Method according to claim 1, in which the solvent from each tract-ionating step after the first fractionating step is recycled to the next preceeding fractionating step.

'6. Method according to claim 5, in which the fraction is precipitated and recovered from the solvent from each step by dissolving a further quantity of said gas in the solvent, thereby precipitating a portion of the extracted fraction, the quantity of additional gas dissolved in the solvent from each step after the first firactionating step being suificient to bring the total dissolved gas quantity in the solvent to an amount substantially equal to the dis-solved gas quantity in the solvent in the next preceding step to which the solvent is to be recycled.

7. Method according to claim 1, in which the extracted fraction is recovered from the solvent from each firactionating step by increasing the temperature of the solvent after said contacting to thereby increase the saturation pressure and precipitate at least a portion of the extracted fraction, and in which, after said recovery, the solvent from at least one of said fractionating steps has its dissolved gas content adjusted to a value substantially equal to the dissolved gas content of a difierent tractionating step, and is thereafter recycled to that fractionating step.

8. Method according to claim 1, in which the said contact is eifected in said fractionating steps by passing said organic material and said solvent in counter-current flow contact, while maintaining a continuous body of one of said organic material and solvent.

9. Method according to claim 1, in which said organic material is admixed with said solvent substantially free from said dissolved gas prior to said contacting and in which said mixture is subjected to said contacting in the first fractionat-ing step.

10. Method according to claim 9, which includes purifying said mixture prior to said contacting.

11. Method according to claim 9, which comprises pressurizing said mixture with said gas prior to said contacting to a pressure below the operating pressure at which said contacting is effected.

12. Method according to claim 1, in which the solvent in each fractionating step contains a lesser quantity of said dissolved gas than the solvent in the next subsequent fractionating ste and in which the recovered extracted fraction is passed from each step to the next subsequent step for said contacting with said solvent.

13. Method according to claim 12, in which the precipitation and recovery of the extracted fraction in each step is efiected by heating the solvent after said contacting to thereby increase the saturation pressure and precipitate at least a portion of the extracted fraction, and in which the solvent, after said recovery from each step after the first fractionating step, is recycled to the next preceding fractionating step.

14. Method according to claim 1, in which the extracted fraction is precipitated and recovered from the solvent from each fractionation step by dissolving a further quantity of said gas in the solvent and increasing the temperature of the solvent after said contacting to increase the saturation pressure and thereby precipitating at least a portion of the extracted fraction.

15. Method according to claim 14, in which said dissolving of the fui'ther quantity of said gas is effected so that the solvent from at least one of said iractionat-ing steps has its dissolved gas content adjusted to a value substantially equal to the dissolved gas content of a different fractionating step and is thereafter recycled to that fractionating step.

References Cited in the file of this patent UNITED STATES PATENTS 2,115,003 Beiswenger Apr. 26, 1938 2,116,188 Churchill May 3, 1938 2,130,147 Milrnore Sept. 13, 1938 2,188,012 Pilat et a1 Jan. 23, 1940 2,188,013 Pilat et a1 Jan. 23, 1940 2,270,674 Pilat et al. Jan. 20, 1942 2,315,131 'Pilat et a1. Mar. 30, 1943 

1. METHOD FOR THE FRACTIONATION OF HIGH MOLECULAR WEIGHT ORGANIC MATERIAL WHICH COMPRISES INTIMATELY CONTACTING THE ORGANIC MATERIAL TO BE FRACTIONAL IN A FRACTIONATING STEP WITH A LIQUID SOLVENT CONTAINING A PREDETERMINED AMOUNT OF A DISSOLVED GAS WHICH DECREASES ITS SOLVENT POWER TO THEREBY SELECTIVELY EXTRACT A FRACTION OF SAID MATERIAL, REMOVING THE SOLVENT WITH THE EXTRACTED FRACTION DISSOLVED THEREIN, SEPARATING AT LEAST A PORTION OF THE EXTRACTED FRACTION FROM THE SOLVENT, CONTACTING AT LEAST ONE OF THE EXTRACTED FRACTIONS AND THE EXTRACTION RESIDUE WITH THE LIQUID SOLVENT CONTAINING A DIFFERENT PREDETERMINED QUALITY OF DISSOLVED GAS IN AT LEAST ONE FURTHER FRACTIONATING STEP TO THEREBY SELECTIVELY EXTRACT A FURTHER FRACTION OF SAID MATERIAL DISSOLVED THERIN AND SEPARATFURTHER EXTRACTED FRACTION DISSOLVED THEREIN AND SEPARATING AT LEAST A PORTION OF THE EXTRACTED FRACTION FROM THE SOLVENT. 